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What is the key functions of a Database Management System (DBMS).

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i) CRUD functions

  • Must enable users to create data structures.
  • Retrieve data from data structures.
  • Update these data structures.
  • And delete data structures

ii) Data dictionary

  • Must support a repository of meta-data.
  • Holds data about structure, relationships and integrity constraints.
  • Holds data about names and authorization privileges associated with users.

iii) Concurrency control

  • Must enable many users to access same data at the same time.
  • And ensure that the database is not left in an inconsistent state when this occurs.

iv) Recovery

  • Must ensure that the database can recover from software or hardware failure that damages it in some way.

 

Describe a data dictionary. Indicate when the data dictionary is used and by whom.

  • A data dictionary is a means for recording the meta-data of some organisation.
  • Also known as system catalog.
  • Typically stores data about the structure of data, relationships between data items, integrity constraints expressed on data, the names and authorization privileges associated with users.
  • The DD effectively implements the three-level architecture of a DBMS.
  • It is a method of recording the data resources and data requirements which can be used during analysis and design as well during implementation.
  • It is the main tool used by the data administrator and database administrator.
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